1. Field of the Invention
The present invention relates to a method for manufacturing a tyre for vehicle wheels.
The invention also relates to an apparatus for the deposition of at least one reinforcing element on a forming support, said apparatus being able to be used to carry out the aforementioned method.
2. Description of the Related Art
Throughout the present description and the subsequent claims, the term “reinforcing element” is used to indicate an element comprising one or more thread-like reinforcing elements, such as textile or metallic cords, incorporated in, or coated with, a layer of elastomeric material.
It should also be specified that, in the present description and in the subsequent claims, the term “elastomeric material”, is used to indicate a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, such a composition also comprises additives such as, for example, a cross-linking agent and/or a plasticizer. Thanks to the provision of the cross-linking agent, such a material can be cross-linked through heating, so as to form the final product.
A tyre for vehicle wheels generally comprises a carcass structure comprising at least one carcass ply formed from reinforcing cords incorporated in an elastomeric matrix. The carcass ply has end flaps respectively engaged with annular anchoring structures arranged in the zones usually identified with the name “beads” and normally formed from a substantially circumferential annular insert on which at least one filling insert is applied in a radially outer position. Such annular structures are commonly identified as “bead cores”.
In a radially outer position with respect to the carcass ply, a belt structure comprising one or more belt layers is associated, said belt layers being arranged radially one on top of the other and having textile or metallic reinforcing cords orientated so that they cross and/or so that they are substantially parallel to the direction of circumferential extension of the tyre.
Between the carcass structure and the belt structure there may be a layer of elastomeric material, known as “under-belt”, having the function of making the radially outer surface of the carcass structure as uniform as possible for the subsequent application of the belt structure.
In a radially outer position with respect to the belt structure a tread band is applied, also made of elastomeric material like-other structural elements forming the tyre.
Between the tread band and the belt structure a so-called “under-layer” made of elastomeric material with suitable properties to ensure a steady union of the tread band itself can be arranged.
On the side surfaces of the carcass structure, respective sidewalls made of elastomeric material are also applied, each extending from one of the side edges of the tread band up to the respective annular structure for anchoring to the beads.
In “tubeless” tyres, the carcass ply is internally coated by a layer of elastomeric material, preferably butylene-based, usually known as “liner”, having optimal characteristics of air impermeability and extending from one bead to the other.
Conventional manufacturing processes of tyres for vehicle wheels essentially provide that the components of the tyre listed above be firstly made separately from each other and then are assembled in a subsequent tyre building step.
The current tendency is, however, that of using manufacturing processes that allow the production and storage of semi-finished products to be minimised or, possibly, eliminated.
More specifically, attention has now turned towards process solutions that allow the individual components of the tyre to be made by directly applying them, according to a predetermined sequence, onto the tyre being built on a forming support, typically toroidal or cylindrical.
For example, in document WO 01/36185 to the same Applicant, the components of the tyre are made on a toroidal support by sequentially depositing on the latter a plurality of reinforcing elements, consisting for example of individual rubberised cords or of rubberized cords grouped in parallel in the form of strip-like elements, particularly used in making the carcass and belt structure, and of continuous elongated elements made of elastomeric material, particularly used for making the other structural components of the tyre, such as, for example, tread band, sidewalls, liners, fillers.
It should be observed that in this case the manufacture of a tyre provides for an automated process substantially without intermediate storage of semi-finished products. In such a process the individual structural components of the tyre described above are manufactured according to a predetermined sequence starting from elongated elements fed by a delivery member that can be operatively associated with an extruder. Thereafter, such elongated elements are deposited on the forming support by means of at least one presser member acting on the elongated element along a pressing direction and mobile with respect to the forming support along a predetermined deposition path.
In patent EP 1 299 825 to the same Applicant, the design step of a tyre automatically generates a plurality of procedures, which substantially reproduce the deposition sequences of all of the structural components, determined in the design step, with which the plant for the manufacture of tyres makes the new models thereof. Such procedures, preferably each containing a deposition sequence of a structural element, are preferably located in a Data Base, from which they are suitably withdrawn to be sent to a corresponding manufacturing unit of the production plant.
The Applicant has perceived that a method like that described in EP 1 299 825 defines a priori the deposition path through software based upon a theoretical deposition profile on which the deposition of the elongated element shall be carried out. In particular, such software, after having received in input a series of information identifying the theoretical deposition profile, processes such information to calculate the spatial coordinates of a series of points defining the deposition path on the forming support.
In practice, the forming support on which the deposition of the reinforcing elements is carried out comprises, as well as the toroidal or cylindrical drum, a plurality of surface layers partially or totally overlapping and partially or totally consisting of elastomeric material. It results from this that, because of the dimensional tolerances of such layers, the actual deposition profile on which the deposition of the reinforcing element shall be carried out is different from the theoretical one used to define the deposition path through the aforementioned software. This can cause a non-optimal deposition of the reinforcing elements on the forming support.